Accumulating evidence indicates that mitochondrial dysfunction contributes to the pathogenesis and/or progression of heart failure by reducing the capacity and/or efficiency of myocardial respiration and increasing production of reactive oxygen species. However, the development of efficacious therapies targeting these perturbations has been limited by an incomplete understanding of their molecular basis. Studies by our laboratory and others indicate that alterations in the metabolism of polyunsaturated fatty acids (PUFAs) may play an important role in these phenomena during development of heart failure by leading to dramatic changes in the fatty acid composition of myocardial phospholipids, particularly cardiolipin (CL) a unique tetra-acyl mitochondrial phospholipid that provides essential support to proteins involved in mitochondrial respiration. CL is optimally functional in the mammalian heart when it contains four linoleic acid (18:2) acyl chains (18:24CL), a conformation generated by a molecular remodeling process requiring 18:2 as a substrate. Decreases in myocardial 18:24CL have been reported in several cardiac pathologies associated with mitochondrial dysfunction, including human dilated cardiomyopathy, and multiple rodent models of heart failure and diabetic cardiomyopathy. Interestingly, in all of these pathologies, decreases in 18:24CL can be accounted for largely by dramatic increases in CL species containing highly unsaturated fatty acid (HUFAs, chiefly, arachidonic acid (20:4) and/or DHA (22:6)), which parallel a global loss of 18:2 and accumulation of these HUFAs in the global myocardial phospholipid fatty acid pool. Recent studies in our laboratory indicate that this remodeling of myocardial phospholipids results from increased expression/activity of delta-6 desaturase (D6D) the rate- limiting enzyme in the biosynthesis of HUFAs from 18:2 and linolenic acid (18:3). Pharmacological inhibition of D6D in spontaneously hypertensive heart failure (SHHF) rats and obese/insulin resistant (ob) mice normalized the CL compositional profile, improved mitochondrial respiratory function, reduced mitochondrial ROS production, and decreased lipoxidative stress to levels near their respective healthy controls. The studies in this proposal will determine if upregulation D6D is sufficient to elicit the mitochondrial dysfunction and cardiac pathology with which it has been associated in these studies, and the extent to which cardiomyocyte D6D (as opposed to liver or "systemic" D6D activity) contributes to the desaturation of CL and membrane fatty acids in the failing heart. We will accomplish these aims by 1) examining the uptake and desaturation of 2H-labeled PUFAs into CL and other phospholipid species of cardiomyocytes isolated from failing and non-failing SHHF rats in the presence and absence of pharmacological or siRNA-mediated inhibition of D6D, and 2) by characterizing the cardiac mitochondrial phenotype of a transgenic mouse with global overexpression of D6D. These studies will shed new light on the mechanism and pathophysiological significance of a widely reported phenomenon that may contribute to the pathogenesis of several prevalent forms of myocardial disease. PUBLIC HEALTH RELEVANCE: Recent studies in our laboratory indicate that changes in the composition of fatty acids in the heart leads to pathologic changes in cardiac mitochondria, the 'powerhouses'of heart cells, that may contribute to the development and/or progression of heart failure. The studies in this proposal will elucidate the mechanisms and pathological importance of these phenomena in hopes of developing new therapeutic strategies for the management of heart disease.